The present invention relates generally to fluid ejection devices.
Inkjet printing is a non-impact printing process in which droplets of fluid are deposited on print media, such as paper, transparency film, label stock, textile and other materials. Essentially, inkjet printing involves the ejection of fine droplets of fluid onto the print media in response to electrical signals generated by a microprocessor.
Generally, there are two types of inkjet printers for achieving fluid droplet ejection: thermal and piezoelectrical. In thermal inkjet printing, electrical resistance heating is used to vaporize the fluid, which is expelled through an orifice in an inkjet printhead (or fluid ejection device) toward the print medium. A microprocessor selects the appropriate resistors to be fired and directs an electrical current thereto to achieve resistive heating and consequential ejection of fluid vaporized by the heating through the orifice associated with the selected resistor. In piezoelectric inkjet printing, the fluid droplets are physically ejected due to vibration of piezoelectric crystals that are energized by electrical signals generated by a microprocessor.
During printing, small fluid droplets are ejected in large quantities, particularly with large throughput printers that use a large fixed array of printheads or a scanning carriage on which a number of inkjet printheads are mounted. In large printers, the printheads typically carry a small supply of fluid across the print zone. The supply is often continuously or intermittently replenished through tubing that extends to the carriage borne printheads from remote or so-called xe2x80x9coff-axisxe2x80x9d stationary reservoirs in the printer. Fine aerosol comprising fluid droplets which do not reach their intended destination on the print medium often collect in undesirable locations on the printer, and on various areas of the printheads which are not normally wiped and cleaned at the printhead service station. Visible amounts of aerosol fluid droplets can be deposited on unintended areas of the print media, as well. The problem is particularly acute when pigment-based rather than dye-based inks are used since pigment-based inks contain a high proportion of undissolved color particles suspended in a volatile organic carrier which has a particularly high tendency to clog the printhead nozzle orifices and can also get on the operator""s hands or clothing. Often, nozzles with smaller orifice diameters have a tendency to crust over or clog. On the other hand, nozzles with larger orifice diameters have larger volume fluid droplets ejected and associated increased power to vaporize the fluid.
It is accordingly desired to reduce aerosol generation in inkjet printing while avoiding clogging of the printhead orifices.
In one embodiment of the present invention a printhead has an orifice plate with an orifice therein, and a heating element that heats fluid and ejects the fluid through the orifice that is associated with the heating element. The orifice has an exit area O, and the heating element has an effective surface area R. In one embodiment, a ratio R/O is below about 2.
Many of the attendant features of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts throughout.